Home Depot will often throw away the wood that is used to bundle lumber together. It's oddball sizes (somewhere around 2x3" and they run maybe
3'- 3 1/2' in length. The most common I see are the pressure treated variety.
Old picnic tables, or other type of tables work well. Go to the Salvation Army or Good Will. Also check out Free Cycle for tables. Old ladders and wood.
The county dump is also a good place to find wood, scrap iron. Ask a wielder if he would consider trading some beer for some wielding.
Do what you like!
Brew what you like!